1. Field of the Invention
The present invention relates to a cathode ray tube used in a computer monitor or a television receiver. It relates in particular to an implosion-protection reinforcing band for the same.
2. Description of the Related Art
A widely known reinforcing band to be mounted around a panel of a cathode ray tube is, for example, a reinforcing band 18 formed in the shape of a closed loop, which is shown in FIG. 6. The reinforcing band 18 is constituted by a band main body 16 that is formed by folding over one side in a width direction of a belt-like metal plate along a fold portion 5 so as to have a partially twofold structure and a joint metal plate 17 that joins end portions of the band main body 16 in their abutting portion.
Being formed with the folded belt-like metal plate, the reinforcing band 18 has a large strength. Thus, it is used in particular for a large cathode ray tube that requires a large force when mounting the reinforcing band around the panel.
However, due to the use of the joint metal plate 17, the reinforcing band 18 described above had following problems.
The joint metal plate 17 was likely to be subjected to an outward force that often was generated in the abutting portion of the band main body 16. In order to suppress this force, in many cases, it was necessary to use a strong material or a thick material for the joint metal plate 17 so that the material or the thickness of the joint metal plate 17 and that of the band main body 16 were different. This caused the problem of increasing material cost or of difficult welding. In addition, a member other than the band main body 16 was used as the joint metal plate 17, increasing the number of components or manufacturing steps as well as the material cost.
It is an object of the present invention to solve the problems described above and to achieve a strong reinforcing band without using a special member so as to provide a cathode ray tube including this reinforcing band.
In order to solve the problems described above, a cathode ray tube of the present invention includes a panel, and a reinforcing band for implosion-protection that is located around a side wall of the panel. The reinforcing band is formed by folding over one side of a belt-like metal plate so as to have a partially twofold structure and by joining both end portions of the belt-like metal plate so as to be in the shape of a closed loop extending along the side wall of the panel. One end portion and the other end portion of the both end portions are joined together so as to achieve a threefold structure in at least one part.
In this manner, the reinforcing band can be joined strongly without using any joint metal plate. Thus, while maintaining a material cost and a manufacturing cost at a low level, it is possible to ensure a sufficient fastening strength of the reinforcing band, thereby achieving the cathode ray tube provided with the reinforcing band having a high implosion-protection effect.
In the above cathode ray tube, it is preferable that in one end portion of the both end portions of the reinforcing band, an edge of a front plate portion extends in a longitudinal direction of the reinforcing band with respect to an edge of a back plate portion, while in the other end portion, an edge of a back plate portion extends in the longitudinal direction of the reinforcing band with respect to an edge of a front plate portion.
This makes it possible to use the material of the reinforcing band without wasting it, thus achieving an overlap easily in which at least one part has the threefold structure.
Furthermore, it is preferable that corners of the both end portions of the reinforcing band are cut off.
Also, it is preferable that an edge of the back plate portion of the reinforcing band that is located closest to the panel has a notch in a portion corresponding to a protrusion on the side wall of the panel.
In this manner, it is possible to prevent the panel side wall from being scratched.